Now that you have learned about your subject you can begin to investigate the inner workings of a pig. You will begin with some observations and then you will begin the dissection of the fetal pig. You should start at the top with the external anatomy. You can then move through the dissection by scrolling down.
(No Dissection Necessary)
Part I - Dissection of the Fetal Pig
First obtain your fetal pig. Lay your pig in your dissection pan and examine the external features of your pig.
You should notice that your pig has a cut on the right side of its neck. This is where the blood was drained from the pig and latex was injected into the arteries and veins of the pig.
VocabularyReview:ventral - towards the bellyDorsal - towards the back
Anterior - to the front
Posterior - to the back
External Anatomy of the Fetal Pig
Click here for a labeled diagram of the external features of the fetal pig.
Look at your pig.
v Large head
v Short Neck
v Trunk with two pairs of appendages.v Tail -which is an extension of the vertebral column
v Umbilical cord
v Nipples (external openings of the mammary glands; found on both male and female pigs)
v Anus (located under the tail)
v Urogenital opening
Females -anterior to the anus; a small fleshy urogenital papilla projects from the urogenital opening
Males -posterior to the umbilical cord.
Observation of the Oral Cavity of the Fetal Pig
Observe thefollowing structures.
v Teeth - undeveloped on both jaws
v Tongue - partly attached to the lower jaw; extends posteriorly and is attached to the bony structure at the back of the oral cavity
2.v Hard palate - ridges of the roof of the mouth, separates the oral cavity from the nasal passages
v Soft Palate - smooth region posteriorto the hard palate.
Observation of the Pharynx of the Fetal Pig
The Pharynx is dorsal to the oral cavity and has three openings: the glottis, the esophagus and the trachea.
Push down on the tongue to open the jaws. You will see a flap pointed dorsally; this is theepiglottis. The epiglottis is the flapthat covers the glottis. The glottis is the opening between the oral cavity and the trachea.
The opening to the esophagus is located posterior and dorsal to the glottis.
Note that theglottis is located very close to the esophagus.
Insert a blunt probe into the glottis. Note that it enters the trachea. Now insert the probe into the esophagus. Notice that the esophagus is underneath the trachea.
The nasopharngeal opening is posterior to the soft palate. The nasopharyngeal opening leads from the oral cavity to the nasal passages.
Observation of the Thoracic Cavity and Abdominal Cavities
Place the fetal pig on its back in the dissecting pan. Tie a cord around one forelimb, bring the cord under the pan, and tie the cord to the other forelimb. Repeat with the hind limbs.
Following the numbered incisionsuse scissors to expose the thoracic and abdominal cavities.
The diaphragm is the structure that separates the thoracic cavity from the abdominal cavity.
Observation of the Neck Region of the Fetal Pig
Locate and observe the thymus gland, larynx, trachea, esophagus and thyroid gland.
The thyroid gland islocated posterior to the larynx and on top of (ventral to) the trachea. The thyroid gland secretes hormones, including thyroxine.
Observation of the Thoracic Cavity of the Fetal Pig
The diaphragm of mammals divides the body into two cavities, the thoracic cavity and theabdominal cavity. The thoracic cavity contains the heart and lungs.
Fold back the chestwall flaps. You will observe a thin membrane that divides the thoracic cavity into three parts: two pleural cavities and one pericardial cavity. Each lung is found in a separate pleural cavity; the lungsare respiratory organs used for gas exchange. The heart is located in the pericardial cavity: it functions as a pump in the circulatory system. Tear the membranes to reveal the heart and lungs.
Examine the lungs. Notice the left lung (on the pig's left side) has three lobes while the right lung has four lobes.
Observation of the Abdominal Cavity of the Fetal Pig
The abdominal cavity and organs are also lined with a membrane. The mesenteric membranes support the organs of the abdominal cavity. If your pig is filled withdark brown fluid (clotted blood) rinse it out in the sink.
The liver is the largest organ in the abdomen. It is dark drown in color and fits snuggly into the diaphragm. The liver performs the following vital functions.
1. produces _____________
2. stores glycogen
3. destroys red blood cells
4. maintains blood glucose levels
5. produces blood proteins
The stomach, small intestines and large intestines are all parts of the ______________ system.
Locate the stomach; it is a large sac located dorsal to the liver on the leftside of the pig. The stomach stores food; it contains several gastric glands that secrete gastric juice, used in the digestion of food. The esophagus carries food from the mouth to the stomach. Find where the esophagus enters the stomach.
Locate the small intestinewhere it exits the stomach. It is a mass of loops and folds that is held together by mesentery. The small intestine receives secretions from the pancreas and gall bladder.
Locate the gallbladder. It is embedded in the liver on the underside of the right lobe. It is a small greenish sac.
Locate the pancreas under the stomach. It is a diffuse gland found in the mesentery between the stomach and the small intestine. The pancreas is both anexocrine gland and an endocrine gland. The pancreas producesand secretes pancreatic juices that aid in the digestion of food.
As an endocrine gland,the pancreas secretes the hormones insulin and glucagon. These hormones are secreted into the blood stream.
Locate the spleen. It is a long, flat reddish organ attached to the stomach by mesentery. The spleen is a lymphoid organ in the immune system. It stores both red and white blood cells.
Open one side of the stomach and note the appearance of the interior surface.
The Cardiovascular System of the Fetal Pig
The heart pumps blood, circulating it to all parts of the body.
Blood is pumped from the heart under pressure. Arteries have thick walls that expand when thepressurized blood enters them. Blood moves away from the heart through the larger arteries and the smaller arterioles. Veins have thinner wallsand valves that prevent blood from flowing backwards in the veins. Blood returns to the heart from the tissues via the larger veins and smaller venules. Blood is pumped away from the heart by the contraction of thebeating heart. Blood is returned to the heart when skeletal musclescontract and press against the veins and venules; this forces blood to move through the veins back toward the heart. Capillaries have exceptionally thin walls; this allows the exchange of materials from the blood with the tissue fluid, which surrounds the capillaries.
Circulation is different in adults and in fetuses. In the adult, blood is oxygenated in the lungs and nutrient molecules enter the blood in the digestive tract. In the fetus, the lungs and digestive system do not function. Fetal blood obtains oxygen and nutrients when diffusion exchange occurs with the mother's blood in the placenta.
Observation of the Blood Vessels of the Fetal Pig
In the fetal pig the pulmonary arteries and veins are not functional.
In your pig thearteries have been injected with red latex and the veins have been injected with blue latex. Refer to Fetal Pig Heart as you observe the following structures.
The systemic circuit carries blood to the entire body. Arteries take oxygenated blood from the heart to the organs; veins take deoxygenated blood from the organs to the heart. The aorta is the major artery, and the venae cavae are the major veins. Using the diagram, locate the following arteries and veins.
The coronary arteries and the cardiac veins can be seen on the surface of the heart. The carotid arteries and the jugular veins serve the neck and head regions ofthe body. Locate these vessels.
The subclavian arteries and veins transport blood to and from the forelimbs. Locate these vessels.
Examine the aorta. It may be necessary to life the left lung to observe the aorta. The aorta may appear white in color due to its thick wall. Trace the aorta as it passes through the diaphragm and into the abdominal cavity.
Lift the liverand the stomach and move it to the side.
Comparison of Blood Vessels
Blood pressure from the pumping heart keeps blood moving in the arteries away from the heart. The thick walls of the arteries expand when blood is pumped into them. The contraction of skeletal muscle causes the blood to flow back tothe heart.
Observation of the Fetal Pig Heart
The Urogenital System of the Fetal Pig
The urinary and reproductive systems are very closely associated in mammals. The organs of each system are particulary associated in males.
The kidneys are located on the dorsal body wall wher they are held in place by connective tissue. The renal artery and vein supply blood to the kidneys.
In males, sperm are produced in the seminiferous tubules of the testes. The sperm arestored in the epididymis and carried through the vas deferens to theurethra. The seminal vesicles, the prostate gland and the bulbourethralgland (Cowper's gland) add fluid to the semen after sperm reach theurethra.
In females, the eggs are produced in follicles of the ovaries. The egg moves from the ovarytot he oviduct where fertilization occurs. The fetus develops in theuterus. The cervix, the opening to the uterus, connects to thevagina. The vagina serves both as the organ of copulation and as the birth canal.
Observation of the Urinary System of the Fetal Pig
Using the diagrams observe and compare the urinary system in both sexes of fetal pigs.
Locate thekidney's. These are large, paired, reddish-brown organs. The kidneys will be found against the muscles of in the back of the pig, held inplace by the peritoneal membrane.
Using the diagram, find the following structures: renal cortex, renal medulla, and the renal pelvis.
Inside the kidney, you can also find the renal pyramid.
Locate the ureters. These are the tubes that leave the kidneys.
Locate the urethra; it leaves the bladder and disappears in the pelvic girdle.
The Male Reproductive System
In the male the testes begin their development in the abdominal caivty, anterior and dorsal to thekidneys. Before birth the testes descend into paired scrotal sacs withinthe scrotum. Each scrotal sac is connected to the body cavity of the fetal pig by an inguinal canal. You should be able to find this openingin your pig. The movement of the testes into the scrotal sacs is reffed to as "descending". Testes descend in both pigs and humans. The testes in your fetal pig will be partially or fully descended. Using this link, locate the following structures in your pig:
Epididymis, vas deferens, penis, inguinal canal, testes, urethra. You may be able to locatethe bulbourethral glands, the proste gland and the small, paired seminalvesicles.
The Reproductive System of Female Fetal Pig
The femalereproductive system consists of the ovaries, the oviducts and the uterus. Eggs are produced in the ovaries and are transported to the uterus by theoviducts (also called the Fallopian Tubes). Fetal development occursin the uterus. In the fetal pig the uterus is not a single organ asin humans. Rather it is partially divided into two extened structurescalled uterine horns which connect with the oviduct. The vagina is thebirth canal and the organ of sexual intercourse.
Using this link, locate the following structures in your pig: ovaries, oviducts, utnerine horn, vagina. The ovaries are small strucutres suspended from the peritoneal wall posteriorto the kidneys. Locate the oviduct; it is a small, coiledtube. The oviduct does not attach to the ovary; it terminates in afunnel-shaped structure that partially encloses the ovary. Observe the uterinehorns; do not confuse the uterine horns with the oviducts. The oviductsare very small and are very close to the ovaries.
The skeletal system of the fetal pig is similar to the human skeleton because both are mammals. However, their are differences in the the types of bones and the shapes of bones because the of the different appearances of both organisms.This body system does not involve any dissection.
Because of the lack of bones in the fetal pig, it will be neccessary to recall the dissection of the chicken leg tolook at some of the features of bones.Click here to see pictures of the features of the bones.Compare the skeleton of the pig withthe skelton of the human.
Fetal pigs have a muscular system that shares some common features with the human muscular system. We will not dissect the fetal pigs muscluar system as the muscles of the fetal pig are very thin and soft. They tear easily. You must recall the chicken leg dissection to remember what muscles look like and how they work.Click here to see pictures from the chicken leg dissection of the muscles.
Using the diagram, locate the musclesthat you have in common with the fetal pig.
Day 2 DissectionActivites
Remove the smallintestine and large intestines by cutting where the small intestine leaves thestomach and where the large intestine becomes the rectum. Carefully cut the membranes holding the coils in the long intestinal section; straighten the intestine. Measure (in mm) the length of the intestinetract.
Intestinal length= mm
2. If have not already done so, you may remove the heart and look at the blood vessels and chambers.
3. If youhave not already done so, you can remove the kidney and cut it with a front cut so that you can observe the inner structures.
4. You can now look at the pig's brain if you would like. This is optional. OPTIONAL.You need to stick the scissors into the eye socket and use that as leverage to slowly and gently chip the brain case. The brain is very very delicate.